Hole 1168A (42°36´S, 144°24´E) was drilled in 2463 m water depth on the western continental slope of Tasmania. Miocene sediments were recognized between Samples 189-1168A-10H-2, 15 cm, and 47X-4, 68 cm, and the stratigraphic distribution of nannofossils is given in Table T1. An expanded Oligocene/Miocene (O/M) boundary section was recovered at Site 1168, and high-resolution biostratigraphic results across this interval are included in Table T2. Key biohorizons are listed in Table T6, along with their sample interval and average depth. The Miocene sediments consist of nannofossil ooze, foraminifer-bearing nannofossil chalk, clay-bearing nannofossil chalk, and nannofossil claystone (Shipboard Scientific Party, 2001b). Calcareous nannofossils are abundant and moderately preserved in all samples.
The Miocene/Pliocene boundary (CN9b/CN10) is placed between Samples 189-1168A-10H-1, 15 cm, and 10H-2, 16 cm, based on the last occurrence (LO) of Triquetrorhabdulus rugosus (5.23 Ma). Discoaster quinqueramus (5.53 Ma), whose LO was used by Okada and Bukry (1980) to mark this boundary, is not recorded in Hole 1168A. The interval from 189-1168A-10H-2, 16 cm, to 12H-6, 15 cm, represents the late Miocene Amaurolithus primus CN9b Subzone of Okada and Bukry (1980), based on the first occurrence (FO) of A. primus. Characteristic nannofossils of this zone are A. primus, Amaurolithus delicatus, Calcidiscus leptoporus, Reticulofenestra minuta, Reticulofenestra minutula, and Reticulofenestra producta. The FO of A. delicatus and the top of the Reticulofenestra pseudoumbilicus >7 µm paracme also occur in this interval.
Several of the late and middle Miocene zones had to be combined, as they are subdivided on the presence of certain discoaster species which are rare to absent in Hole 1168A. Discoaster loeblichii and Discoaster surculus were not consistently present in Hole 1168A, whereas Discoaster berggrenii and Discoaster neorectus were not recorded. Therefore, the D. berggrenii Subzone CN9a and the D. neorectus Subzone CN8b were combined, and the bottom of the R. pseudoumbilicus paracme >7 µm is used to approximate the base of this combined zone. According to Young (1998), this event is slightly older than the FO of D. neorectus and D. loeblichii. The combined zone extends down to Sample 189-1168A-15X-2, 15 cm, and is characterized by the low abundance of R. pseudoumbilicus >7 µm and abundant C. leptoporus, Coccolithus pelagicus, R. minuta, R. minutula, and Reticulofenestra perplexa. The closely spaced FO of Sphenolithus abies, the LO of Minylitha convallis, and a sharp increase in the abundance of R. producta may indicate a condensed section at ~129 meters below seafloor (mbsf). Above this depth, discoaster diversity increases and an influx of diatom microfossils was noted.
The base of the Discoaster bellus CN8a Subzone was approximated by the FO of M. convallis, as Discoaster hamatus was not recorded in Hole 1168A. Subzone CN8a extends down to Sample 189-1168A-17X-4, 15 cm (152.70 mbsf). Catinaster calyculus was not recorded in Hole 1168A, and only one specimen of Catinaster coalitus was noted, causing the combination of the D. hamatus CN7 Zone and the C. coalitus CN6 Zone. The LO of Coccolithus miopelagicus is used to approximate the base of Zone CN6 in the absence of C. coalitus (Raffi and Flores, 1995). This interval extends down to Sample 189-1168A-20X-5, 15 cm (183.0 mbsf), and is characterized by common C. leptoporus, C. pelagicus, Reticulofenestra gelida, R. minutula, and R. perplexa.
The base of the CN5b Discoaster kugleri Subzone was recognized by the LO of Cyclicargolithus floridanus and is placed between Sample 189-1168A-22X-2, 15 cm, and 22X-3, 15 cm (197.8 mbsf). This interval is characterized by C. leptoporus, Calcidiscus macintyrei, C. pelagicus, R. pseudoumbilicus, R. gelida, R. minuta, R. minutula, and by few Calcidiscus tropicus and Sphenolithus compactus.
The LO of Sphenolithus heteromorphus is placed between Sample 189-1168A-26X-7, 15 cm, and 26X-7, 15 cm (242.2 mbsf), marking the base of the C. miopelagicus CN5a Subzone. The assemblage includes abundant C. leptoporus, C. macintyrei, C. pelagicus, R. pseudoumbilicus, R. gelida, R. minuta, and R. minutula. C. tropicus, Discoaster spp. 6-rayed, Geminilithella rotula, Helicosphaera paleocarteri, Pyrocyclus hermosus, Reticulofenestra haqii, S. compactus, and Sphenolithus moriformis are commonly present. The LO of Calcidiscus premacintyrei (221.5 mbsf) and the last common occurrence (LCO) of C. floridanus (236.2 mbsf) occur within Subzone CN5a.
The S. heteromorphus CN4 and the Helicosphaera ampliaperta CN3 Zones were combined, as H. ampliaperta was present in only two samples in Hole 1168A. The base of the combined zone is marked by the FO of S. heteromorphus at 293.8 mbsf (Samples 189-1168A-32X-2, 15 cm, through 32X-3, 15 cm). This interval contains abundant C. pelagicus, C. floridanus, R. haqii, and R. minuta. Common species are C. leptoporus, C. macintyrei, C. premacintyrei, Cyclicargolithus abisectus, Discoaster spp. 6-rayed, G. rotula, H. paleocarteri, Pyrocyclus orangensis, S. compactus, and S. moriformis. The LO of Sphenolithus belemnos, which is used in the Martini (1971) zonal scheme to mark the base of his H. ampliaperta NN4 Zone (roughly equivalent to Okada and Bukry's CN3 Zone), occurs at 299.6 mbsf, slightly below the FO of S. heteromorphus.
The FO of S. belemnos marks the base of the S. belemnos CN2 Zone and occurs between Samples 189-1168A-34X-3, 15 cm, and 34X-4, 15 cm (313.9 mbsf). Abundant C. pelagicus, C. floridanus, R. minuta, and R. minutula were recorded in this interval.
The ~5-m.y.-long Triquetrorhabdulus carinatus CN1 Zone is subdivided into three subzones by Okada and Bukry (1980), based on the FO of Discoaster druggii (CN1a/CN1b) and the acme event of C. abisectus (CN1b/CN1c). D. druggii was not recorded in any Leg 189 sediments, and the acme event of C. abisectus is poorly described and difficult to quantitatively determine (Young, 1998). Recent work has refined the biostratigraphy of this interval with several additional bioevents (Olafsson, 1989; deKaenel and Villa, 1996; Maiorano and Monechi, 1998). Unfortunately, much of this work has described tropical to subtropical species, which were not consistently recorded in Leg 189 sediments or could not be identified because of moderate preservation. The FO of C. tropicus <6 µm was listed by deKaenel and Villa (1996) as occurring just above the Zone NN1/NN2 (Martini, 1971) boundary (approximate to the Subzone CN1b/CN1c boundary). The FO of C. tropicus is used here to estimate the Subzone CN1b/CN1c boundary and occurs between Samples 189-1168A-43X-5, 2 cm, and 43X-5, 40 cm (402.71 mbsf). The CN1c Subzone contains common C. pelagicus, C. floridanus, Discoaster spp. 6-rayed, R. haqii, R. minuta, and R. minutula.
The base of the CN1b Discoaster deflandrei Subzone is approximated here by the LO of Sphenolithus capricornutus at 437.39 mbsf (Samples 189-1168A-47X-2, 78 cm, to 47X-2, 120 cm). This interval is similar to the CN1c Subzone except for the absence of C. tropicus and the increased abundance of Helicosphaera bramlettei and Helicosphaera compacta. The Oligocene/Miocene boundary (CN1a/CP19) is placed at 439.94 mbsf between Samples 189-1168A-47X-4, 40 cm, and 47X-4, 68 cm, based on the LO of Reticulofenestra bisecta bisecta.
Hole 1170A (47°09´S, 146°02´E) was drilled in 2704 m water depth on the South Tasman Rise (Fig. F1), south of the modern STF. Miocene sediments were recognized between Samples 189-1170A-15H-4, 60 cm, and 42X-3, 110 cm, and the stratigraphic distribution of nannofossils is given in Table T3. Key biohorizons are listed in Table T6, along with their sample interval and average depth. The Miocene sediments consist of nannofossil ooze, foraminifer-bearing nannofossil chalk, nannofossil chalk, and nannofossil claystone (Shipboard Scientific Party, 2001d). Calcareous nannofossils were abundant and moderately preserved in all samples.
The Miocene/Pliocene boundary (CN9b/CN10) is placed between Samples 189-1170-15H-3, 60 cm, and 15H-4, 60 cm (129.32 mbsf), based on the LO of T. rugosus. The late Miocene A. primus CN9b Subzone, based on the FO of A. primus, contains abundant C. leptoporus, C. pelagicus, R. gelida, R. minutula, and R. perplexa.
Coring disturbance in some sections of this interval was quite extreme (Shipboard Scientific Party, 2001d), and core sections that were disturbed (based on visual examination of core photos) were excluded from this report. The FO of A. primus, A. delicatus, and the top of the R. pseudoumbilicus >7 µm paracme occur between the bottom of Core 17H and the top of Core 19X. Coring disturbance was extreme in Core 18H, the last advanced piston corer (APC) core taken in Hole 1170A, and the entire core was unsuitable for analysis. This complicated the determination of the base of the A. primus Subzone, which is tentatively placed between Samples 189-1170A-17H-CC and 19X-1, 60 cm. A possible hiatus exists across this boundary, but the core disturbance complicates interpretation of such an event (for further discussion, see Stickley et al., this volume).
The Okada and Bukry (1980) D. berggrenii CN9a Subzone and the D. neorectus CN8b Subzone were combined, as at Site 1168, and the base of Subzone CN8b is approximated by the bottom of the R. pseudoumbilicus >7 µm paracme event. This event occurs between Samples 189-1170A-21X-2, 60 cm, and 21X-3, 60 cm, at 179.15 mbsf. This interval is characterized by the low abundance of R. pseudoumbilicus >7 µm and the presence of C. leptoporus, C. pelagicus, R. minuta, R. minutula, and R. perplexa. Low numbers of C. macintyrei, Discoaster spp. 6-rayed, S. moriformis <6 µm, and T. rugosus were recorded in this interval.
The lack of marker species forced the combination of several late Miocene zones. The next discernible marker event is the LO of C. miopelagicus, used here to mark the base of the C. coalitus CN6 Zone between Samples 189-1170A-25X-2, 60 cm, and 25X-3, 60 cm (217.55 mbsf). Common C. leptoporus, C. pelagicus, R. gelida, R. minutula, and R. perplexa are present throughout this interval. Discoasters are less abundant in this interval than in the overlying sediments.
The LO of C. floridanus marks the base of the D. kugleri CN5b Subzone between Samples 189-1170A-28X-4, 60 cm, and 28X-5, 60 cm (249.35 mbsf). This interval contains abundant C. pelagicus, R. gelida, R. minutula, and R. perplexa. The FO of R. perplexa is coincident with the base of this subzone. Discoasters are absent throughout this interval.
Sphenolithus heteromorphus was not recorded in situ in Hole 1170A; therefore, the top of the S. heteromorphus CN4 Zone (13.52 Ma) is approximated by the LCO of C. floridanus (13.2 Ma). The CN4/CN5a boundary is placed between Samples 189-1170A-31X-4, 60 cm, and 31X-5, 60 cm (278.15 mbsf). Calcidiscus leptoporus, C. pelagicus, R. gelida, and R. minutula are abundant in this interval.
The lack of consistently present H. ampliaperta forced the combination of Zones CN4 and CN3, as at Site 1168. The FO of C. premacintyrei (17.4 Ma) between Samples 189-1170A-35X-2, 60 cm, and 35X-3, 60 cm (312.95 mbsf), is used to roughly approximate the base of the H. ampliaperta CN3 Zone, as S. heteromorphus (FO = 18.2 Ma) and S. belemnos (FO = 18.3 Ma) were not recorded in situ in Hole 1170A. The FO of C. premacintyrei is easily detected, and this bioevent has the potential to be a key marker in mid- to high-latitude areas where sphenoliths are generally absent. This interval contains abundant C. pelagicus, C. floridanus, and R. minutula. Common species are C. leptoporus, C. premacintyrei, C. tropicus, Discoaster spp. 6-rayed, G. rotula, H. paleocarteri, and R. gelida.
The base of the S. belemnos CN2 Zone could not be identified in Hole 1170A. The FO of C. tropicus between Samples 189-1170A-41X-5, 60 cm, and 41X-6, 60 cm, places the base of the CN1c Subzone at 375.9 mbsf. The combined CN1a/CN1b Subzone continues down to 382.25 mbsf (Samples 189-1170A-42X-3, 110 cm, through 42X-4, 60 cm), where the LO of R. bisecta bisecta occurs. Within the CN1a/CN1b Subzone the simultaneous LOs of Clausicoccus obrutus, Hughesius tasmaniae, and Reticulofenestra stavensis were noted at ~380 mbsf, indicating a hiatus/condensed interval just above the O/M boundary. Magnetostratigraphic (Stickley et al., this volume) and benthic oxygen isotope (Pfuhl and McCave, this volume) work suggest continuous though condensed sedimentation across the O/M boundary.
Hole 1171A (48°30´S, 149°07´E) was drilled in 2148 m water depth on the South Tasman Rise (Fig. F1) in subantarctic waters. Hole 1171A was cored to 124.4 mbsf and bottomed in upper Miocene sediments (Shipboard Scientific Party, 2001e). To construct a complete Miocene section, samples were also taken from Hole 1171C (48°30´S, 149°07´E; 2148 m water depth) beginning at 110 mbsf. Miocene sediments were recognized between Samples 189-1171A-7H-1, 15 cm, and 189-1171C-28X-4, 15 cm, and the stratigraphic distribution of nannofossils is given in Table T4. Key biohorizons are listed in Table T6, along with their sample interval and average depth. The Miocene sediments consist of nannofossil ooze, foraminifer-bearing nannofossil ooze, diatom-bearing nannofossil ooze, clay-bearing nannofossil ooze, nannofossil chalk, and foraminifer-bearing nannofossil chalk (Shipboard Scientific Party, 2001e). Calcareous nannofossils are abundant and moderately preserved in all samples.
The Miocene/Pliocene boundary (CN9/CN10) is placed between Samples 189-1171A-6H-7, 15 cm, and 7H-1, 15 cm (54.5 mbsf), based on the LO of T. rugosus. The base of the late Miocene A. primus CN9b Subzone was recognized based on the FO of A. primus at 65.57 mbsf. At the same depth, one sample contained rare M. convallis. Rare occurrences of M. convallis have been reported from Prydz Bay (Pospichal, 2002) and the South Atlantic at 42.5°S (Marino and Flores, 2002). The LO of M. convallis and the FO of A. primus indicate a brief hiatus across the CN9a/CN9b boundary. Amaurolithus primus was the only ceratolith recognized in Hole 1171A. The A. primus Subzone extends through Sample 189-1171A-8H-2, 15 cm, and is characterized by abundant C. leptoporus, C. pelagicus, R. gelida, R. minuta, R. minutula, R. perplexa, and R. pseudoumbilicus. The top of the R. pseudoumbilicus >7 µm paracme event occurs within this interval.
As at Sites 1168 and 1170, the D. berggrenii CN9a Subzone was combined with the D. neorectus CN8b Subzone. The base of this combined interval was approximated by the bottom of the R. pseudoumbilicus >7 µm paracme event, which occurs between Samples 189-1171A-9H-2, 15 cm, and 9H-3, 15 cm (76.0 mbsf). This interval contains abundant C. leptoporus, C. pelagicus, R. gelida, and R. minutula.
Late Miocene Zones CN8a, CN7, and CN6 were combined, as several marker species were absent from Site 1171 sediments. The base of the C. coalitus CN6 Zone is approximated by the LO of C. miopelagicus between Samples 189-1171C-16X-2, 15 m, and 16X-3, 15 cm (137.65 mbsf). The simultaneous LOs of C. miopelagicus and C. floridanus at 137.65 mbsf suggests that the CN5b D. kugleri Subzone is missing in Hole 1171C. Alternative explanations of the co-occurrence may be the spotty distribution of C. miopelagicus in Hole 1171C, the LOs at this site may be climatically rather than evolutionarily induced, or the LOs of these species are most likely diachronous (Wei and Wise, 1992; Raffi, et al, 1995; deKaenel and Villa, 1996; Backman and Raffi, 1997; Maiorano and Monechi, 1998). However unreliable these events may be, the interpretation of a hiatus at this depth is supported by diatom data (see Stickley et al., this volume).
Sphenolithus heteromorphus was recorded in only one sample, and therefore the top of the S. heteromorphus Zone (CN4) is approximated by the LCO of C. floridanus, as in Hole 1170A. The CN4/CN5a boundary is placed between Samples 189-1171C-18X-5, 15 cm, and 18X-6, 15 cm (160.6 mbsf). Abundant C. leptoporus, C. pelagicus, R. minuta, R. minutula, and R. pseudoumbilicus were recorded in the CN5a C. miopelagicus Subzone. The LO of C. premacintyrei and the FOs of R. gelida and R. perplexa occurred within this interval.
As in Hole 1170A, the S. heteromorphus CN4 and the H. ampliaperta CN3 Zones are combined. The base of the combined CN3/CN4 Zone was roughly approximated by the FO of C. premacintyrei, as S. heteromorphus was rare and S. belemnos was not present in Hole 1171C. The base the combined zone is placed at 197.2 mbsf between Samples 189-1171C-22X-4, 15 cm, and 22X-5, 15 cm. Calcidiscus leptoporus, C. pelagicus, C. floridanus, R. minuta, and R. minutula are abundant throughout this interval. Calcidiscus fuscus, C. premacintyrei, Discoaster 6-rayed spp., P. orangensis, R. haqii, and S. moriformis were commonly recorded.
As at Site 1170, the base of the S. belemnos CN2 Zone could not be determined and CN2 was combined with the D. druggii CN1c Subzone. This combined zone contains abundant C. pelagicus, C. floridanus, R. minuta, and R. minutula, with commonly occurring C. abisectus, Discoaster 6-rayed spp., P. orangensis, R. haqii, and S. moriformis. A hiatus encompassing the early Miocene CN1a and CN1b Subzones is indicated by the FO of C. tropicus and the LO of R. bisecta bisecta, both at 253.47 mbsf (between Samples 189-1171C-28X-4, 15 cm, and 28X-CC). This interpretation of the O/M boundary is in agreement with other biostratigraphic data (Stickley et al., this volume).
Hole 1172A (43°58´S, 149°70´E) was drilled in 2622 m water depth on the East Tasman Plateau (Fig. F1). Miocene sediments were recognized between Samples 189-1172A-8H-CC, and 37X-4, 15 cm, and the stratigraphic distribution of nannofossils is given in Table T5. Key biohorizons are listed in Table T6, along with their sample interval and average depth. The Miocene sediments consist of nannofossil ooze, nannofossil chalk, foraminifer-bearing nannofossil chalk, and nannofossil claystone (Shipboard Scientific Party, 2001f). Calcareous nannofossils were abundant and moderately preserved in all samples.
The Miocene/Pliocene boundary (CN9b/CN10) is tentatively placed between Samples 189-1172A-8H-CC, and 10H-3, 15 cm (79.34 mbsf), based on the combined LO of D. quinqueramus (5.53 Ma), used by Okada and Bukry (1980) to mark this boundary, and the LO of T. rugosus (5.23 Ma). This interval contained extremely disturbed cores, with large sections of flow-in (Scientific Shipboard Party, 2000f), making the exact placement of the Miocene/Pliocene boundary problematic (for further discussion see Stickley et al., this volume). The interval from 189-1172A-10H-3, 15 cm, to 13H-7, 15 cm, represents the late Miocene A. primus CN9b Subzone, based on the FO of A. primus. Characteristic nannofossils of this zone are A. primus, A. delicatus, C. leptoporus, R. minuta, and R. minutula. The FO of A. primus and A. delicatus occur simultaneously with the top of the R. pseudoumbilicus >7 µm paracme and indicate a brief hiatus/condensed section at ~120 mbsf.
Several late and middle Miocene zones had to be combined in Hole 1172A, as key discoaster species were sporadically recorded or could not identified because of calcite overgrowth. Therefore, the D. berggrenii Subzone CN9a and the D. neorectus Subzone CN8b were combined and the base was approximated by the bottom of the R. pseudoumbilicus >7 µm paracme. This combined zone extends down to 163.7 mbsf (between Sample 189-1172A-18H-4, 15 cm, and 18H-5, 15 cm) and is characterized by the low abundance of R. pseudoumbilicus >7 µm and the presence of C. leptoporus, C. pelagicus, R. minuta, R. minutula, and R. perplexa. Low numbers of C. macintyrei, Discoaster spp. 6-rayed, S. moriformis <6 µm, and T. rugosus are present in this interval.
Discoaster hamatus, C. calyculus, C. coalitus, and M. convallis were not recorded in Hole 1172A sediments, causing the combination of the late Miocene D. bellus CN8a, the middle Miocene D. hamatus CN7, and the C. coalitus CN6 Zones. The base of Zone CN6 is estimated by the LO of C. miopelagicus between Sample 189-1172A-26X-3, 15 cm, and 26X-4, 15 cm (234.0 mbsf). This interval is characterized by common to abundant C. leptoporus, C. pelagicus, R. gelida, R. minutula, and R. perplexa.
The base the D. kugleri CN5b Subzone is marked by the LO of C. floridanus between Samples 189-1172A-27X-3, 15 cm, and 27X-4, 15 cm (243.6 mbsf). This short interval contains common C. leptoporus, C. pelagicus, R. minutula, R. pseudoumbilicus, and abundant R. gelida.
The LO of S. heteromorphus is placed in Sample 189-1172A-31X-3, 15 cm (281.5 mbsf), marking the base of the C. miopelagicus CN5a Subzone. This subzone is dominated by C. leptoporus, C. pelagicus, R. pseudoumbilicus, R. gelida, R. minuta, and R. minutula. Scarce to rare nannofossils are represented by C. macintyrei, C. miopelagicus, Discoaster spp. 6-rayed, G. rotula, P. hermosus, R. haqii, and S. compactus. The LO of C. premacintyrei (12.7 Ma) and the LCO of C. floridanus (13.2 Ma) occur within this interval.
The S. heteromorphus CN4 and the H. ampliaperta CN3 Zones were combined, as H. ampliaperta was not recorded in Hole 1172A. The base of this combined zone is marked by the FO of S. heteromorphus between Samples 189-1172A-34X-4, 15 cm, and 34X-5, 15 cm (311.9 mbsf). Cyclicargolithus floridanus, Discoaster spp. 6 rayed, R. haqii, and R. minutula are common to abundant throughout this interval.
Sphenolithus belemnos, which marks the base of the S. belemnos CN2 Zone was not recorded in Hole 1172A. This suggests that the CN2 Zone is not present in Hole 1172A and that a hiatus encompassing the S. belemnos CN2 Zone exists. It is possible that S. belemnos was ecologically excluded from Site 1172 as at Sites 1170 and 1171. In the absence of corroborating data from other microfossil groups or magnetostratigraphy for a hiatus and as the ecological requirements of this extinct species are not well known, the author assumes that no hiatus exists.
The early Miocene T. carinatus Zone is subdivided based on the FO of C. tropicus. This occurs between Samples 189-1172A-36X-4, 15 cm, and 36X-5, 15 cm, and is used to approximate the CN1b/CN1c boundary. A hiatus is suggested at this depth by the co-occurrence of C. tropicus and two early Miocene planktonic foraminifers (for details see Stickley et al., this volume). The early Miocene sediments are characterized by abundant to common C. pelagicus, C. floridanus, Discoaster 6-rayed, R. haqii, R. minuta, R. minutula, and S. compactus. The Oligocene/Miocene boundary (CP19/CN1) is placed at 340.46 mbsf between Samples 189-1172A-37X-4, 15 cm, and 37X-4, 117 cm, based on the LO of R. bisecta bisecta.